What is fentanyl used for medically?

In this article:

• How fentanyl works
• Is fentanyl dangerous?
• What is fentanyl used for?
• Fentanyl side effects and warnings
• Contraindications
• Side effects

In this article

• How fentanyl works
• Is fentanyl dangerous?
• What is fentanyl used for?
• Fentanyl side effects and warnings
• Contraindications
• Side effects

Fentanyl has received a lot of attention—but not for its proven medical benefits. It’s part of the ongoing opioid crisis and contributes to thousands of overdoses every year. That might have soured the public opinion of it, and that’s understandable, but it’s also important to know that fentanyl has several important, legitimate uses—particularly when it comes to pain relief. Here are all the details on fentanyl’s role in anesthesia and pain management.  

How fentanyl works

Fentanyl is an opioid analgesic, just like tramadol, oxycodone, methadone, and codeine. That means its primary purpose is to reduce pain. It does this by attaching to opioid receptors, which are located on the parts of the brain that control pain and emotion. It blocks these receptors, interrupting signals to the brain that would trigger a pain response. However, it works a lot quicker than other opioids, and it has a short half-life, making it useful as a short-term intervention for procedures like surgeries.

Is fentanyl dangerous?

Fentanyl is a powerful drug, and it can be very safe when it is used with the oversight of a healthcare professional. Medical professionals are extremely cautious and precise when prescribing fentanyl, and they actively monitor their patients for respiratory depression and hypoxia during fentanyl treatment.

“Fentanyl is much more potent than other opioids, 100 times more than morphine. This means that doses are much smaller. We use micrograms rather than milligrams, and small amounts can have big effects,” says Ryan Marino, MD, Associate Professor at the Case Western Reserve University School of Medicine.

A study from Acta Anaesthesiologica Scandinavica on intravenous fentanyl administered by ambulance personnel found that it was both safe and effective. Likewise, an older study from Anesthesia & Analgesia found that it was both effective and well-tolerated when administered for post-surgical pain.

But outside the hospital, where drugs aren’t accurately measured or used as cautiously, it’s a different story. “When fentanyl is present in unregulated form—like illicit fentanyl sold on the street—it is impossible to know what the dose or amount is, and much easier for tiny changes to cause significant effects, including overdose,” Dr. Marino says. “The difference is that pharmaceutical fentanyl comes in a known, labeled dose and is free of adulterants and impurities (or other drugs). Additionally, the use in healthcare is always in monitored settings to ensure that adverse effects don’t happen or are treated promptly.”

Another significant issue with illegally manufactured fentanyl is that it’s often found in counterfeit pills, which resemble other prescription drugs. Dealers may mix it with drugs like cocaine, methamphetamine, or heroin because it’s potent and cheap, delivering an intense high at a low cost. But that mixing is imprecise, skyrocketing the risk of overdose and death. In fact, in 2022, the Drug Enforcement Administration found that 60% of fentanyl-laced counterfeit prescription pills contained a lethal dose of the drug.

What is fentanyl used for?

All of fentanyl’s uses revolve around pain management, but there are several different circumstances where it can help. Here are the most common uses of medical fentanyl.

Anesthesia

Given its quick action and exceptional pain relief, fentanyl works very well in anesthesiology. In fact, it has largely replaced morphine as the go-to opioid anesthetic. “Anesthesiologists use it every single day on almost every patient undergoing surgery,” says Zachary Fisk, MD, MBA, founder of Acute Pain Therapies. “It is thought of by anesthesiologists almost like a primary ‘currency,’ where the anesthesiologists understand how fentanyl acts very intuitively, and then use that understanding as a baseline for their interpretation of other opioid analgesics.”

For anesthesia, fentanyl is typically administered intravenously. The dosage depends on the patient’s body weight and indication, but it’s usually a single 20–50 mcg/kg dose—administered via IV—for general anesthesia and 2–50 mcg/kg as an anesthesia adjunct. For individuals undergoing a complicated procedure, healthcare providers may increase the dose to 150 mcg/kg and administer it with a muscle relaxant. Sometimes it’s also combined with propofol for anesthesia.

Postoperative and intraoperative pain

Opioids are widely used as surgical pain medications, but fentanyl works slightly differently than drugs like morphine and Dilaudid. Specifically, “Its onset of action is faster than those agents, with an onset time of one minute and a peak effect of five minutes. This makes fentanyl extremely useful for minimizing the body’s pain response to surgical stimuli and for quickly reducing pain during and immediately after surgery and in the recovery area,” Dr. Fisk says. “It is very useful to add in slowly over the course of a procedure to achieve an optimal level of analgesia for the surgery itself; this is impossible with slower onset analgesics.”

For those reasons, fentanyl has become the most common drug for intravenous, intraoperative anesthesia in the world. After surgery, the typical dosage is 50–100 mcg every one to two hours as needed. Or, with an IV, it could be 0.5–1.5 mcg/kg per hour as needed.

Epidurals

Approximately 70–75% of pregnant women use epidural analgesia during childbirth, and fentanyl is a common drug for both analgesia and epidural anesthesia. A 2024 study from the American Journal of Obstetrics & Gynecology found that epidural fentanyl substantially decreased labor pain during vaginal delivery, and a separate study from 2019 found that using fentanyl as an epidural administration didn’t have any effects on breastfeeding.

“Fentanyl is safe during labor and safe in any supervised medical use. Some people may be more sensitive to the effects of drugs like fentanyl or may have more adverse effects than others, and it is possible to be allergic to fentanyl products,” Dr. Marino says. “By targeting the nerves at the spine it is possible to get better pain control and fewer of the systemic side effects from intravenous administration, and usually at a lower dose as well.”

As always, the ideal dosage depends on the situation, although a 2017 study published in Anesthesia concluded that 50 mcg and 100 mcg doses were more effective than 20 mcg. For labor analgesia, doctors sometimes opt to combine fentanyl with a local anesthetic like bupivacaine or ropivacaine. Fentanyl/bupivacaine has shown effectiveness, although a 2015 study found that fentanyl/ropivacaine had a lower incidence of motor blocks.

Acute pain

In some cases, healthcare providers might use fentanyl off-label to treat “breakthrough pain,” acute pain that occurs despite taking other opioids—often in cancer patients who are undergoing treatment. Studies have shown that using fentanyl this way is both safe and effective (when it’s administered by a healthcare provider). In addition to intramuscularly or intravenously, doctors may administer it as a nasal spray, lozenge, or buccal tablet. Intranasally, the typical dose of fentanyl is 1–2 mcg/kg per hour as needed, with a maximum dosage of 100 mcg. Lozenge doses can be 200–1600 mcg, while buccal tablets are 100–800 mcg.

Thanks to fentanyl’s rapid onset, it’s also effective for acute pain caused by trauma. Research has confirmed that it’s just as effective as morphine but works even faster. One study from the Journal of Clinical Medicine even said it’s “clearly superior to other opioids in initial resuscitation and treatment as it has minimal effects on hemodynamic status and does not cause central nervous system depression.”

Chronic severe pain

Fentanyl is sometimes prescribed for chronic pain from cancer or other conditions. However, it’s only administered via a transdermal patch. Since patients can use them at home, and it’s so easy to overdose, these patches help the body absorb the drug at a steady, safer rate. They range from 12 mcg/hr to 100 mcg/hr, depending on the patient’s condition, level of pain, and medical history. When using fentanyl, there is always a risk of respiratory depression, hypoxia, and death and this risk increases when the patient is not being monitored by a medical professional. 

Fentanyl side effects and warnings

In a medical setting, administered by a healthcare provider, fentanyl is typically safe, but that doesn’t mean it’s a good option for everyone. It has certain contraindications and side effects that might cause serious complications.

Contraindications

Considering fentanyl’s reputation as an illicit drug, its risk of misuse likely won’t come as a surprise. Like other opioids, it can cause dependence, which can lead to abuse. Yet because fentanyl is so much more potent than many other opioids, abuse can quickly turn into overdose. According to the National Center for Drug Abuse Statistics, more than half of all overdose deaths in the United States involve fentanyl. That’s why it’s crucial for patients to tell their doctors about any past experience with substance use disorder or if there are others with substance abuse disorders who will have access to the medication.

Even when it’s used in a clinical setting, fentanyl may cause respiratory depression, making breathing more difficult. That’s why it’s not prescribed for people with conditions that affect breathing, like asthma, COPD, obstructive sleep apnea, and obesity with hypoventilation. People who have liver failure, a known intolerance to fentanyl, or a hypersensitivity to drug delivery excipients like sodium chloride should also not take fentanyl, according to the National Institutes of Health.

Side effects

Side effects are different for everyone, and they could be mild or nonexistent, but it’s still good to know all the possibilities. Some of the most common fentanyl side effects include gastrointestinal issues (such as stomach pain and nausea), sleep disturbances, feelings of malaise, skin problems, psychiatric effects (anxiety or depression), nervous system effects, loss of appetite, low heart rate, low blood pressure (hypotension), and shortness of breath.

There are also more serious side effects, which include overdose, allergic reactions, respiratory depression, central nervous system depression, seizures, cardiac arrest, and delirium, among others.

Bottom line 

Fentanyl has earned a scary reputation as a medication that kills people because of its serious overdose risk, and while that’s true on the street (where it’s commonly abused) it’s important to remember that the drug is both safe and extremely useful in controlled, observant medical settings. As a powerful opioid pain reliever, it’s a versatile drug in a healthcare setting, effective for postoperative pain, anesthesia, epidural infusion, acute breakthrough pain, chronic pain, and more. Still, anyone concerned about the drug’s warnings or side effects should speak with their healthcare provider before receiving it.